Preheat your oven to 275°F. Tear the brioche bread into approximately 1 inch chunks. You'll want the chunks to all be about the same size. Spread them out in an even layer on a baking sheet, and bake in your preheated oven for 45 minutes, until the bread is completely dried out.  Remove from the oven when finished.

Combine the chicken broth, eggs, parsley, sage, rosemary, salt and pepper in a medium-sized mixing bowl. Whisk together until fully mixed and then set aside.

In a large frying pan, melt the stick of butter over low to medium heat. Add the chopped celery and onion. Sauté until the celery and onion are soft and fragrant, about 10 minutes. Remove from heat and set aside. 

Increase the oven temperature to 350°F. Grease the inside of a 9" x 13" baking dish with butter. 

Transfer the bread to a large mixing bowl. Pour the bowl of liquid ingredients (broth, eggs, herbs, seasonings) and the melted butter, sautéed onions and sautéed celery over top of the brioche bread cubes.  Thoroughly mix the ingredients together, until they're fully incorporated and all of the chunks of bread have become saturated in liquid.  

Transfer the stuffing mixture to your greased casserole dish.  Cover tightly with aluminum foil and bake for 40 minutes in your preheated oven.  Uncover and bake for an additional 25-30 minutes, until the top of the stuffing is brown and crispy. 

Remove from the oven, let cool for about 15 minutes, serve and enjoy!